IMF’s, Solids, and Liquids Mr. Kinton Honors Chemistry

Recall What do you remember about solids and their structure? What about liquids and their structure? Intra-particle forces: Ionic, Covalent, and Metallic bonds

Intermolecular Forces The forces that exist between molecules Weaker than Intra-particle forces Determine the properties of liquids such as boiling point Low boiling point=weaker IMF’s High boiling point=stronger IMF’s Same holds true for solids and their melting point

Types of Intermolecular Forces There are 3 types of intermolecular forces in neutral molecules: London-Dispersion forces Dipole-dipole forces Hydrogen Bonding The 3 are referred to as the van der Waals forces Each are electrostatic in nature

London Dispersion Forces Caused by electrons repelling one another Creates a temporary dipole Strongest in larger molecules Polarizability: the ability of an atoms electric field to be distorted Exist in all molecules

Dipole-Dipole Forces Positive end of one molecule is near the negative end of another molecule Only effective when polar molecules are near each other Dipole-Dipole forces occur between only polar molecules

Hydrogen Bonding Special type of attraction between a Hydrogen atom and either a F, O, or N atom of an adjacent molecule Causes higher than usual melting/boiling points Strongest intermolecular force

Ion-Dipole Force Attraction between an ion and a polar molecule Increases based on charge of the ion or the dipole moment Important in the formation of solutions

Melting/Boiling Points

IMF Flow Chart

Classification of Matter Solids Liquids Definite shape and volume Rigid, not compressible Molecules are held tightly together Definite molecular arrangement Definite volume Takes shape of container Not compressible Molecules close together but move rapidly

Classification of Matter Gases Key Terms Also known as vapor Does not have a definite shape and volume Can be compressed Molecules are far apart Move at a fast pace Atoms: small building blocks of matter Molecules: two or more atoms joined together

You Try! Classify the following as a solid, liquid, or gas: Oxygen Hand Soap Eraser Nacho Cheese Gold Chlorine

Vapor Pressure Vapor Pressure – the pressure exerted by a gas in the space above a liquid or solid (must have a constant value At any temperature the movement of particles into the gas phase occurs continuously. As time passes the number of particles in the gas phase increases, thus increasing the chances that a particle will be recaptured by the surface of the liquid (or solid.) Eventually the number of particles escaping equals the number recaptured.

Dynamic Equilibrium Dynamic equilibrium is the condition in which two opposing processes are occurring simultaneously at equal rates. A liquid and its vapor are in equilibrium when evaporation and condensation occur at equal rates. The equilibrium vapor pressure of a liquid is the pressure exerted by its vapor when the liquid and vapor states are in dynamic equilibrium. Also called vapor pressure

Vapor Pressure and Temperature Vapor pressure increases with higher temperature. Higher temperature equals more energy and therefore the more particles escaping the surface. Temperature – A measure of the average kinetic energy of the particles in a substance.

Vapor Pressure and Volatility Volatility – The ability of a substance to evaporate. Substances that are extremely volatile will evaporate more quickly. (Ex: gasoline, alcohols) These substances have weak forces holding the particles together. Substances with high volatility have a high vapor pressure (at room temperature) and therefore have a _____ (low/high) boiling point.

Melting Point The melting point and the freezing point of a substance are always equal The melting point occurs at the point where the vapor pressure of the solid and the liquid are equal.

Boiling Point A liquid boils when its vapor pressure equals the external pressure acting on the surface of the liquid. Boiling point increases with increasing external pressure Normal boiliing point – The boiling point of a liquid at standard pressure (1 atm = 760 torr.)

Vapor Pressure Graph At what temperature will water boil at 320 torr? What is the normal boiling point for diethyl ether? How low must the pressure be for ethanol to boil at 40 Celsius?

Phase Diagrams Phase diagram: plot of pressure vs. Temperature summarizing all equilibria between phases. Given a temperature and pressure, phase diagrams tell us which phase will exist. Any temperature and pressure combination not on a curve represents a single phase.

Phase Diagram

Phase Diagrams Curves of a phase diagram: Vapor-pressure curve: (line AB)the equilibrium between the liquid and the gas phases. Generally as pressure increases, temperature increases. Curve AC: the equilibrium between the solid and gas phase; the variation in the vapor pressure of the solid as it sublimes at different tempertures. Melting point curve: (line AD) the equilibrium between the solid and liquid; the change in melting point of the solid with increasing pressure.

Phase Diagrams Points of a phase diagram: Triple point: temperature and pressure at which all three phases are in equilibrium. All three phases exist at this point. Critical point: critical temperature and pressure for the gas. Beyond this point the liquid and gas phases become indistingushable. Normal melting point: melting point at standard pressure (1 atm, 760 torr, 101.3 kPa). Always located on the melting point curve Normal boiling point: boiling point at standard pressure (1 atm, 760 torr, 101.3 kPa). Always located on the vapor-pressure curve.

Phase Diagrams of H20 and CO2 As pressure increases, the solid phase is favored if the solid is more dense than the liquid.

Solutions Are they substances or mixtures? IMF’s interact between the solute and the solvent Solute: substance being dissolved Solvent: substance doing the dissolving

How do Solutions form Attractive forces between solute and solvent are comparable to the individual forces Solvation: when ions are separated and surrounded by a solvent Hydrations: solvation when water is the solvent This is a physical change

Energy Of Solution Formation

Energy Changes Exothermic Endothermic heat is released to the surroundings Spontaneous Feels warm heat is absorbed from the surroundings Can be spontaneous Feels cold

Entropy The amount of disorder in a system Processes that increase entropy tend to occur spontaneously Solution formation is favored when entropy increases

Solutions and Solubility Solubility: amount of solute needed to form a saturated solution in a solvent Saturated: solution that is in equilibrium with undissolved solute Unsaturated: less solute is dissolved than possible in a solution Supersaturated: occurs when a solution is heated, more solute is added, then cooled

Solubility Curves

Factors Affecting Solubility Solute-Solvent Interactions Pressure Effects Temperature Effects

Solute-Solvent Interactions Increase when there are stronger attractions between solute and solvent Hence “like dissolves like” Miscible: liquids that mix in all proportions Immiscible: liquids that do not dissolve each other

Pressure Effects Only impacts gases in solution Increasing pressure causes an increase in gas concentration

Temperature Effects Increase in temperature causes an increase in solid solubility Increase in temperature causes a decrease in gas solubility

Ways of Expressing Concentration Qualitatively quantitatively Dilute: relatively small concentration Concentrated: large concentration of solute Mass percentage Mole fraction Molarity Molality

Colligative Properties Properties that depend on the concentration of solute particles As the number of solute particles increase so do the colligative properties as well 4 Colligative Properties Vapor Pressure Boiling-Point Elevation Freezing-Point Depression Osmosis

Vapor Pressure Pressure exerted by a vapor in a closed container Nonvolatile: no measurable vapor pressure Volatile: has a measurable vapor pressure Adding a nonvolatile will lower the vapor pressure

Boiling Point Elevation/Freezing Point Depression Based on the presence of nonvolatile in the solution Adding a nonvolatile increases the boiling point, but lowers the freezing point Adding an electrolyte increases the effect

Osmosis Net movement of solvent toward a solution with higher concentration Stops when the osmotic pressure can stop the movement of the solvent